The rapid diagnosis of infectious diseases is important for the management of ill patients and for the containment of disease outbreaks. Most previously developed assay systems have made use of either immunoassay or nucleic acid hybridization procedures for the detection of micro-organisms. Immunoassay and hybridization techniques offer advantages for use in microbial diagnosis; however no single method has proven to be ideal for the detection of all microbial agents. We propose to combine solid phase capture, nucleic acid amplification, and immunoassay methodologies to develop a single assay system for the detection of microbial pathogens. Target nucleic acids will be specifically bound to solid phase surfaces by hybridization to RNA probes. Following the removal of contaminating nucleic acids and other materials by washing, the bound nucleic acids will be eluted and amplified by means of cyclical enzymatic reactions. The amplified nucleic acids will then be quantitated by means of solid phase enzyme immunoassay procedures. This assay format will allow for the sensitive amplification and detection of specific microbial genomic sequences in human body fluids without interference from extraneous materials. Furthermore, the utilization of familiar enzyme immunoassay procedures for reaction quantitation will allow for the utilization of the assay system in a wide range of clinical and research laboratory environments. The capture amplification assays will be developed for the detection of pathogenic agents of enteric, respiratory, and sexually transmitted diseases. Initial target organisms will include rotaviruses, influenza viruses and Chlamydia trachomatis. The sensitivity and specificity assays will be evaluated in a step-wise fashion using purified nucleic acids and a range of homologous and heterologous microorganisms. The clinical efficiency and specificity of the assay systems will then be evaluated utilizing serial samples obtained from well-defined study populations. The successful development of these assays will be followed by the development of analogous assays for additional microbial agents. The productive application of these assays might improve the medical care of patients with suspected infections and minimize disease transmission within hospital environments.